HoDoKu is a Sudoku generator/solver/analyzer. It has many human-style techniques (singles, subsets, LCs, fish, wings, uniqueness, coloring, chains, and ALS) and a powerful analyzer (manage multiple solutions for one Sudoku).

ff3sudoku is an add-on that features an engine for playing Sudoku puzzles. It can generate random puzzles, but it also detects and imports Sudokus from several Web sites, including websudoku.com, sudokupuzz.com, sudoku.com.au, and others. There is also a stand-alone version working in Firefox 3+ and GoogleChrome.

Binary Puzzle Solver in Ruby is an automated solver for Binary Puzzles (a kind of logic game) featured on http://www.binarypuzzle.com/. The solver contains an API and a commandline program and explains why it thinks the player should place a 0 or a 1 in the box. Although it contains only a subset of the moves the authors could think of and does not use backtracking, it was able to solve all the puzzles from binarypuzzle.com which the authors tried.